Pressure-controlled breathing aid

ABSTRACT

The ventilation module (8) regulates the inspiratory pressure (P) according to an inspiratory pressure order (AI). A control module (9) compares the breathed volume at each cycle (VTI) with a minimum volume order (VTImini) and varies the pressure order (AI) in the direction tending to maintain the breathed volume (VTI) just over the minimum (VTImini), but keeping the pressure order (AI) within the interval comprised between the two extreme values (AImini, AImaxi). Utilization to combine the advantages of the pressure mode ventilation with those of the volumetric ventilation.

RELATED APPLICATIONS

This is a continuation of Ser. No. 08/793,956, filed Mar. 12, 1997 nowU.S. Pat. No. 5,921,238.

The present invention relates to a pressure-controlled breathing aid.

Breathing aid devices—or ventilation devices—currently used inmechanical ventilation can be divided into two main groups, namelyvolumetric devices characterized by the supply of a specified volume ineach respiratory cycle, and pressure-controlled devices characterized bythe provision of a specified pressure in each respiratory cycle.

Volumetric devices have the advantage of guaranteeing a specifiedbreathed volume, but they have major disadvantages. In particular, theyexpose the patient to risks of barotrauma as they tend to apply pressurewhich increases at the end of insufflation. Furthermore, the patientrisks not being matched to the device in the sense that the respiratoryreflexes of the patient can appear at different times from those atwhich the volumes imposed by the device finish being supplied.

On the contrary, pressure-controlled devices allow bettersynchronization of the patient with the device and avoid the risk ofbarotrauma since the maximum pressure supplied is known in advance. Onthe other hand, the volume supplied to the patient in each cycle and thebreathed volume are not guaranteed.

The purpose of the present invention is to propose a breathing aiddevice which combines the advantages of both of the known ventilationmodes discussed above.

According to the invention, the pressure mode breathing aid device,comprising means for supplying breathable gas to an inspiratory branchof a patient circuit at an inspiratory pressure, is characterized by:

-   -   means of measuring the breathed volume,    -   means of comparing the breathed volume with a command, and    -   regulation means to increase the inspiratory pressure in the        case of a breathed volume lower than the command, and to reduce        the inspiratory pressure in the case of a breathed volume higher        than the command.

Thus, the pressure is adjusted in a direction tending to provide thepredetermined volume applied as a command. In this way a volume isguaranteed without taking the risk of increasing the pressure in anuncontrolled manner, nor of creating the particular risk of mismatchbetween the breathing timing of the patient and that of the device. Inparticular, the invention is perfectly compatible with devices of thetype described in FR-A-2 695 830 in which the device detects therespiratory reflexes of the patient in order to change from inspiratoryphases to expiratory phases and vice-versa.

In order to prevent any risk of barotrauma, it is advantageous toprovide means of setting a maximum predetermined pressure which thepressure applied to the patient will not be able to exceed even if thevolume supplied is insufficient.

It is also advantageous to provide a signalling device or other alarmdetecting the simultaneous occurrence of insufficient volume and thesetting of the pressure at its maximum predetermined value, in order tosignal this situation of the device's inability to provide the breathedvolume set as a command.

In the framework of the present invention, the expression “breathedvolume” is used to denote both the volume of the breathable gas inspiredor expired per unit time and the volume or quantity of gas inspired orexpired per breathing cycle.

Preferably, the adjustment means apply to the inspiratory pressure apressure variation which is equal in percentage to the differencebetween the inspiratory volume and the command.

However, in the case where an extreme value of pressure is predeterminedand if the application of such a variation would result in exceeding theextreme value, the new inspiratory pressure is made equal to the extremevalue of the pressure.

Other features and advantageous of the invention will furthermore emergefrom the following description relating to non-limitative examples.

In the accompanying drawings:

FIG. 1 is a block diagram of a first embodiment of the device accordingto the invention;

FIG. 2 is an operational flowchart of the regulating means of the deviceof FIG. 1; and

FIGS. 3 and 4 are two block diagrams similar to FIG. 1 but relating totwo embodiments of the device according invention.

In the example shown in FIG. 1, the breathing aid device comprises apatient circuit 1 which itself comprises a patient connection 2, namelya facial or nasal mask, or an intubation or tracheotomy tube, connectedto an inspiratory branch 3 and to an expiratory branch 4 by theintermediary of a bidirectional branch 5. The expiratory branch 4comprises an expiration device 6 which, in a way which is not shown,comprises an expiration valve and means of controlling this valve. Theexpiration valve is closed during the inspiratory phases of thepatient's breathing. During the expiratory phases of the patient'sbreathing, the expiration valve can either be open so that the patientexpires at atmospheric pressure, or it can operate like a dischargevalve to oblige the patient to expire at a certain predetermined excesspressure.

The inspiratory branch 3 is connected, at its end furthest from the mask2, to a unit 8 for ventilation through inspiratory aid which comprisesmeans, such as an adjustable speed motor-turbine set, for supplyingbreathable gas through the inspiratory branch 3 at an adjustablepressure, in the direction of the mask 2, means of detecting thepatient's respiratory reflexes, for example from instantaneous flow ratevariations, and means of controlling the expiration valve of theexpiration means 6 and an inspiration valve placed in the inspiratorybranch 3 in order to open the inspiration valve and to close theexpiration valve during the inspiratory phase, and to close theinspiration valve and to release the expiration valve during theexpiratory phases. Thus, in the inspiratory phase, the patient isconnected in a gas-tight manner with the inspiratory branch 3, and thevolume flowing in the inspiratory branch 3 corresponds to the volume ofgas inspired. And during the expiratory phases, the patient is connectedin a gas-tight manner with the expiratory branch 4 and the volumeflowing in the expiratory branch 4 corresponds to the volume of gasexpired.

Such inspiratory aid devices, or inspiratory aid devices of the samekind are described in the prior art, in particular in FR-A-2 695 830.

The ventilation unit 8 can comprise pressure control means by means ofwhich the pressure P detected in the inspiratory branch 3 by a detector10 is compared with a pressure command AI in order to adjust, forexample, the speed of rotation of the motor-turbine set in the directiontending to make the pressure P equal to the command AI.

According to the invention, the breathing aid device comprises means 11of regulating the patient's breathed volume. The regulating means 11comprise a control unit 9 for controlling the pressure command AI whichthe ventilation unit 8 must apply to the inspiratory branch 3 during theinspiratory phases.

The regulating means 11 furthermore comprise a unit 12 for measuring thevolume VTI inspired by the patient during each breathing cycle. The unit12 provides the control unit 9 with a signal indicative of the volumeVTI. The control unit 9 comprises an input 13 for receiving the signalVTI, and three inputs 14, 16, 17, allowing the user of the device toenter a minimum breathed volume command into the control unit, in theform of a minimum inspired volume per cycle VTImini, a minimuminspiratory pressure command AImini, and a maximum inspiratory pressurecommand AImaxi.

In general, the control unit 9 compares the measured volume VTI with thecommand VTImini and adjusts the pressure command AI in the directiontending to bring the measured volume VTI towards the command VTImini,without however causing the command AI to move outside of the rangeincluded between the two extreme values AImini and AImaxi. Within thisrange, the control unit 9 tends to increase the command AI when themeasured volume VTI is lower than the command VTImini, and to reduce thepressure command AI in the opposite case.

When starting up the device, the commands VTImini and AImini are chosensuch that the breathed volume VTI is established at a value higher thanVTImini when the pressure command AI is equal to AImini. Thus, if thepatient breathes as expected, the pressure command AI stabilises atAImini with a breathed volume above the minimum command VTImini. It isonly in the event of a breathing anomaly or incident, for example apartial obstruction of the breathing channels, that the measuredbreathed volume VTI is likely to become lower than VTImini, thus causingan increase in the command AI generated by the control unit 9. When thebreathing becomes normal again, the breathed volume again becomes higherthan the command VTImini, such that the control unit 9 returns thepressure command AI more or less rapidly to the value AImini.

The flowchart used by the control unit 9 will now be described ingreater detail with reference to FIG. 2. At the start, AI is made toequal to AImini (step 18).

Then, at the end of each breathing cycle, or during each expiratoryphase, the measurement VTI of the volume inspired during the precedinginspiratory phase is acquired (step 19) and is then compared with thecommand VTImini by the test 21. If the measured volume VTI is greaterthan or equal to VTImini, in other words if the volume inspired by thepatient is satisfactory, a test 22 determines if the pressure command AIis or is not greater than the minimum AImini. If the pressure command isequal to the minimum, the conditions are therefore ideal (volume atleast equal to the minimum, minimum pressure) and the sequence thereforereturns directly to step 19 for acquiring the next inspired volumemeasurement. In the opposite case, advantage will be taken of the factthat the inspired volume is satisfactory in order to attempt to reducethe pressure command by a step 23 in which there is applied to thepressure command AI, expressed in relative value, a variation equal inpercentage and opposite in sign to the difference between the measuredinspired volume VTI and the command VTImini. The formula is such that,in the particular case in which the measured volume VTI is equal toVTImini, no modification is applied to the pressure command AI (0%variation).

Returning now to the test 21 on the measured volume VTI, if the latteris lower than the command VTImini, an attempt will be made to increasethe pressure command AI in order to assist the patient more. But priorto this, by a test 24, it will be checked that the pressure command AIhas not already reached the maximum AImaxi. If the answer is yes, analarm is triggered (step 26) to indicate the necessity of an urgentintervention.

On the other hand, if the pressure command AI is not yet equal toAImaxi, the sequence returns as before to step 23 in which there will beapplied to the command AI a variation equal in percentage and oppositein sign to the difference between the measured volume VTI and thecommand VTImini.

Before actually applying the command AI, reduced or increased such as ithas been computed in step 23, to the input of the ventilation unit 8, itwill firstly be checked, by a test 27, that the new computed AI valuedoes not exceed the maximum AImaxi and, by a test 28, that it is notless than the minimum AImini.

If the new AI value has gone beyond one or other of these extremevalues, the command AI which will be applied to the ventilation unit 8will be equal to the extreme value in question (steps 29 and 31).

The example shown in FIG. 3 will only be described where it differs withrespect to the example shown in FIG. 1.

In the example of FIG. 3, the breathed volume is no longer measured bymeans of the volume inspired in each cycle but by means of the volumeVTE expired in each cycle. For this purpose, the VTI measuring unit 12in the inspiratory branch 3 has been eliminated and it has been replacedby a VTE measuring unit 32 in the expiratory branch 4.

The minimum breathed volume command applied to the control unit 9 istherefore the command VTEmini for the volume expired per cycle, in orderto be able to be compared directly with the measurement provided by theunit 32.

It can be advantageous to select, case by case, measurement of theinspired volume or measurement of the expired volume. This is thesolution proposed by the embodiment shown in FIG. 4, which will bedescribed only where it differs with respect to the example shown inFIG. 1.

The measuring unit 42 is this time installed in the bidirectional branch5 of the patient circuit 1 and it comprises means 43 of selecting thedirection of flow in which the volume is to be measured. In accordancewith this selection, the unit 42 provides, by choice, a measurement ofVTI or of VTE. In accordance with the operating mode of the measuringunit 42, the control unit 9 interprets the input applied at 14 as aninspired volume command or as an expired volume command. There is nolonger any measuring unit in the inspiratory branch 3 nor in theexpiratory branch 4.

In all of the described embodiments, the speed of execution of theflowchart in FIG. 2 is sufficient for the measurement carried out ineach breathing cycle to make it possible to correct the pressure appliedduring the following inspiratory phase. When the measurement is based onthe expired volume, it is however possible that the pressure correctionwill occur only during, and not from the start, of the followinginspiratory phase.

The invention is applicable to all ventilators capable of measuring thevolumes delivered and of automatically controlling the value of theinsufflation pressure.

The invention is applicable to all methods of ventilation using pressurecontrol, and in particular to “inspiratory aid” and “controlledpressure” methods. Inspiratory aid is a method consisting in maintaininga substantially constant pressure in the patient circuit during theinsufflation, the patient initiating the start and end of theinsufflation by his respiratory reflexes. The controlled pressure methodis identical to the inspiratory aid method except that the patient doesnot initiate the end of the insufflation, the latter being determined bya fixed time.

It would also be conceivable for the control unit, instead of adjustingthe pressure command AI applied to the ventilation unit, to adjust, forexample, the speed of rotation of the motor turbine set, or theelectrical power supplied to it. It would then be possible to avoidabnormal pressures in the inspiratory branch 3 by comparing the pressurein the inspiratory branch 3 with limits such as AImini and AImaxi, andby initiating a corrective modification of the speed or of the power ofthe motor turbine set in the case of exceeding, or of risk of exceedingsuch limits.

1. A breathing aid device, comprising: a patient connection; aninspiratory branch in fluid communication with said patient connection,said inspiratory branch including an inspiration valve; an expiratorybranch in fluid communication with said patient connection and saidinspiratory branch; means for controlling expiration in fluidcommunication with said expiratory branch, said means for controllingexpiration including an expiration valve; means for detecting pressureoperatively connected to said inspiratory branch; means for ventilatingin fluid communication with said inspiratory branch, said means forventilating including means for supplying a breathable gas through saidinspiratory branch at an adjustable pressure, said means for ventilatingfurther including means for controlling the inspiration valve and theexpiration valve, wherein the inspiration valve is closed duringexpiration and the expiration valve is closed during inspiration, saidmeans for ventilating further including pressure control means forcomparing a pressure command to a pressure signal provided by said meansfor detecting pressure and for adjusting the pressure of the means forsupplying; and means for regulating a patient's breathed volume, saidmeans for regulating including means for controlling volume and meansfor measuring volume, wherein the means for controlling volume providesthe pressure command to the pressure control means, and wherein themeans for measuring volume provides a signal indicative of a measuredvolume of breathed gas to the means for controlling volume.
 2. Thedevice of claim 1, wherein said patient connection includes a facialmask.
 3. The device of claim 1, wherein said patient connection includesa nasal mask.
 4. The device of claim 1, wherein the means for supplyingbreathable gas includes an adjustable speed motor-turbine set.
 5. Thedevice of claim 1, wherein the means for controlling volume includes aninput for a minimum inspired volume per cycle, an input for a minimuminspiratory pressure command, and an input for a maximum inspiratorypressure command, wherein the means for controlling volume compares themeasured volume from the means for measuring volume with the minimuminspired volume per cycle and adjusts the pressure command in thedirection tending to bring the signal from the means for measuringvolume toward the minimum inspired volume per cycle, and wherein themeans for controlling volume maintains the pressure command within therange of the minimum inspiratory pressure command and the maximuminspiratory pressure command.
 6. A breathing aid device, comprising: apatient connection; an inspiratory branch in fluid communication withsaid patient connection, said inspiratory branch including aninspiration valve; an expiratory branch in fluid communication with saidpatient connection and said inspiratory branch; an expiration device influid communication with said expiratory branch, said expiratory deviceincluding an expiration valve; a pressure detector operatively connectedto said inspiratory branch and disposed on said patient connection; aventilation unit in fluid communication with said inspiratory branch,said ventilation unit including a source of breathable gas at anadjustable pressure, said ventilation unit further including a valvecontroller configured to close the inspiration valve during expirationand to close the expiration valve during inspiration, said ventilationunit further including a pressure controller for comparing a pressuredetected by said pressure detector to a pressure command and foradjusting the pressure of the source of breathable gas; and a regulatorfor regulating a patient's breathed volume, said regulator including acontrol unit and a measuring unit, wherein the control unit provides thepressure command to said ventilation unit, and wherein the measuringunit provides a signal indicative of a measured volume of breathed gasto the control unit.
 7. The device of claim 6, wherein the source ofbreathable gas at an adjustable pressure includes an adjustable speedmotor-turbine set.
 8. The device of claim 6, wherein the control unitincludes an input for a minimum inspired volume per cycle, an input fora minimum inspiratory pressure command, and an input for a maximuminspiratory pressure command, wherein the control unit compares themeasured volume from the measuring unit with the minimum inspired volumeper cycle and adjusts the pressure command in the direction tending tobring the signal from the measuring unit toward the minimum inspiredvolume per cycle, and wherein the control unit maintains the pressurecommand within the range of the minimum inspiratory pressure command andthe maximum inspiratory pressure command.
 9. A breathing aid device,comprising: a patient connection; an inspiratory branch in fluidcommunication with said patient connection, said inspiratory branchincluding an inspiration valve; an expiratory branch in fluidcommunication with said patient connection and said inspiratory branch,said expiratory branch including an expiration valve; a pressuredetector operatively connected to said inspiratory branch; a source ofbreathable gas at an adjustable pressure in fluid communication withsaid inspiratory branch; a valve controller for opening and closing theinspiration valve and the expiration valve, wherein the valve controllercloses the inspiration valve during expiration and closes the expirationvalve during inspiration; a pressure controller for comparing a pressuredetected by said pressure detector to a pressure command and foradjusting the pressure of the source of breathable gas; a control unitfor providing the pressure command to said pressure controller; and ameasuring unit for providing a signal to the control unit indicative ofa measured volume of breathable gas detected per breathing cycle to thepatient connection.
 10. The device of claim 9, wherein said control unitincludes a minimum inspired volume per cycle, an input for a minimuminspiratory pressure command, and an input for a maximum inspiratorypressure command, wherein said control unit compares the measured volumefrom said measuring unit with the minimum inspired volume per cycle andadjusts the pressure command in the direction tending to bring thesignal from said measuring unit toward the minimum inspired volume percycle, and wherein the control unit maintains the pressure commandwithin the range of the minimum inspiratory pressure command and themaximum inspiratory pressure command.